A particle beam processing device is commonly used to expose a substrate or coating to highly accelerated particle beams, such as an electron beam (EB), to cause a chemical reaction, such as a polymerization, on the substrate or coating.
In EB processing, energetic electrons can be used to modify the molecular structure of a wide variety of products and materials. Electrons can be used, for example, to alter specially designed liquid coatings, inks and adhesives. For example, during EB processing, electrons break bonds and form charged particles and free radicals, which can cause polymerization to occur.
Liquid coatings treated with EB processing may include printing inks, varnishes, silicone release coatings, primer coatings, pressure sensitive adhesives, barrier coatings and laminating adhesives. EB processing may also be used to alter and/or enhance the physical characteristics of solid materials such as paper, substrates and non-woven textile substrates, all specially designed to react to EB treatment.
A particle beam processing device generally includes three zones, i.e., a vacuum chamber zone where a particle beam is generated, a particle accelerator zone, and a processing zone. In the vacuum chamber, a tungsten filament(s) is heated to, for example, about 2400K, which is the thermionic emission temperature of tungsten, to create a cloud of electrons. A positive voltage differential is then applied to the vacuum chamber to extract and simultaneously accelerate these electrons. Thereafter, the electrons pass through a thin foil and enter the processing zone. The thin foil functions as a barrier between the vacuum chamber and the processing zone. Accelerated electrons exit the vacuum chamber through the thin foil and enter the processing zone, which is usually at atmospheric conditions.
Electron beam processing devices that are commercially available at the present time generally operate at a minimum voltage of approximately 125 kVolts. Additionally, U.S. Patent Publication No. 2003/0001108, the disclosure of which is incorporated by reference herein, describes an EB unit that operates at lower voltages, such as 110 kV or lower. Materials that can be treated with this lower voltage electron beam equipment (110 kV or lower) include coatings, inks, and laminating adhesives for flexible food packaging.
One challenge facing those using electron beam processing for curing either overprint varnishes or laminating adhesives on conventional solvent or water-based inks is ink adhesion. Either the overprint varnish or the adhesive has little or no wettability or adhesion to the ink, or the ink itself lacks cohesiveness and can split or delaminate from the base film upon applying any force such as experienced during a standard T-peel test or tape adhesion test.
Accordingly, there exists a need to continue developing materials that can be treated with EB processing.